Ultra-high fiber density micro-duct cable with extreme operating performance

ABSTRACT

A micro-duct cable includes a center member and a plurality of buffer tubes surrounding the center member. A plurality of fibers are disposed in each of the plurality of buffer tubes. Each of the plurality of buffer tubes contains greater than or equal to 24 fibers. The micro-duct cable further includes a cable jacket surrounding the plurality of buffer tubes and the center member. A maximum outer diameter of the cable is less than 13 millimeters and a modulus of elasticity of the cable is greater than or equal to 800 kpsi.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority to U.S. Provisional ApplicationSer. No. 62/141,503, filed on Apr. 1, 2015 and which is incorporated byreference herein in its entirety.

BACKGROUND

1. Technical Field

The present disclosure is related to an ultra-high density fiber opticmicro-duct cable, and more particularly, to a cable which may include288 fibers and which is configured to be inserted in a micro-duct havingan inner diameter of 13 mm or less, and that is capable of withstandinghigh tensile and compressive loads and extreme temperature ranges.

2. Description of the Related Art

As the demand for bandwidth needed to support communications devicescontinues to increase, fiber networks continue to grow and expand. Anexisting method for installing fiber optic cables is to blow or jet thecable into a micro-duct. In these cases, the micro-duct limits the cableconstruction that can be installed. To overcome this, manufacturers havedeveloped small diameter, lightweight cables with high fiber density foruse in the ducts. However, as noted in Telcordia's Generic Requirementsfor Optical Fiber and Optical Fiber Cable (GR-20, Issue 4), “The smallsize of the micro-duct cables results in generally lower tensilestrength, crush resistance, and the like.” As such, technicians musttake special care while installing traditional duct cables. Further,existing constructions of high fiber count cables often have a limitedoperating temperature range, so they are not suitable in extremetemperature environments. While some high count constructions arecommercially available, their construction limits the operatingperformance, specifically the tensile load, compression resistance andoperating temperature ranges.

SUMMARY

Exemplary embodiments of the present disclosure address the problemsand/or disadvantages of the related art technology described above.Although the present invention is not required to overcome all of thedisadvantages described above, the exemplary implementations of thepresent disclosure may address the above disadvantages, and furtherdisadvantages not described above, or may not overcome any of theproblems listed above while still providing enhancement to the relatedart.

In accordance with one embodiment, a micro-duct cable is provided. Themicro-duct cable includes a center member and a plurality of buffertubes surrounding the center member. A plurality of fibers are disposedin each of the plurality of buffer tubes. Each of the plurality ofbuffer tubes contains greater than or equal to 24 fibers. The micro-ductcable further includes a cable jacket surrounding the plurality ofbuffer tubes and the center member. A maximum outer diameter of thecable is less than 13 millimeters and a modulus of elasticity of thecable is greater than or equal to 800 kpsi.

In exemplary embodiments, each of the plurality of buffer tubes has anouter diameter of less than or equal to 3.1 millimeters and an innerdiameter of less than or equal to 2.5 millimeters. Further, in exemplaryembodiments, each of the plurality of buffer tubes has a compressionresistance of greater than or equal to 4.8 N/cm.

In exemplary embodiments, the fibers have a helical bend radius ofgreater than or equal to 40 mm, such as greater than or equal to 50 mm.Further, in exemplary embodiments, the cable has a coefficient ofthermal expansion of less than or equal to 2×10⁻⁵/° C. and a contractionwindow in excess of 0.25%.

In accordance with another embodiment a micro-duct cable is provided.The micro-duct cable includes a center member, and a plurality of buffertubes surrounding the center member. A gel is disposed within each ofthe plurality of buffer tubes, and a plurality of optical fibers aredisposed in each of the plurality of buffer tubes. Each of the pluralityof optical buffer tubes has an outer diameter of less than or equal to3.1 millimeters and an inner diameter of less than or equal to 2.5millimeters and contains greater than or equal to 48 optical fibers. Themicro-duct cable further includes a cable jacket surrounding theplurality of buffer tubes and the center member. A maximum outerdiameter of the cable is less than 13 millimeters and a modulus ofelasticity of the cable is greater than or equal to 800 kpsi.

In exemplary embodiments, each of the plurality of buffer tubes has anouter diameter of less than or equal to 3.1 millimeters and an innerdiameter of less than or equal to 2.5 millimeters. Further, in exemplaryembodiments, each of the plurality of buffer tubes has a compressionresistance of greater than or equal to 4.8 N/cm.

In exemplary embodiments, the fibers have a helical bend radius ofgreater than or equal to 40 mm, such as greater than or equal to 50 mm.Further, in exemplary embodiments, the cable has a coefficient ofthermal expansion of less than or equal to 2×10⁻⁵/° C. and a contractionwindow in excess of 0.25%.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects of the present invention will become moreapparent from the following description of exemplary embodiments, takenin conjunction with the accompanying drawings of which:

FIG. 1 is a cross-sectional view of a cable according to a firstembodiment of the present disclosure.

FIG. 2 is a cross-sectional view of a cable according to anotherembodiment of the present disclosure.

FIG. 3 is a cross-sectional view of a cable according to anotherembodiment of the present disclosure.

FIG. 4 is a cross-sectional view of a cable according to anotherembodiment of the present disclosure.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, exemplary embodiments will be described in greater detailwith reference to the accompanying drawings.

In the following description, same reference numerals are used for thesame elements when they are depicted in different drawings. Elements aredescribed in detail in order to assist in an understanding of exemplaryembodiments. Thus, it is apparent that exemplary embodiments may becarried out without those specifically-defined elements. Detaileddescriptions of known elements are omitted for clarity and conciseness.

In a first embodiment, as shown in FIG. 1, an ultra-high fiber densitymicro-duct cable 10 comprises multiple buffer tubes 3, each of which isconfigured to contain a plurality of fibers 9 and which may furthercontain a thixotropic gel 8. For example, a buffer tube may containgreater than or equal to 24 fibers, such as between 24 fibers and 72fibers, such as in exemplary embodiments 48 fibers per tube. A fiber maybe, for example, an optical fiber 9. A buffer tube 3 may, for example,be formed from a polypropylene or polybutylene terephthalate. The buffertube 3 may be designed to yield a compression resistance greater than4.8 N/cm. The fibers may be color coded and identified by ring markingsor colored thread yarns. The buffer tubes 3 are cabled over a fiberglassreinforced plastic rod or center member 5 with a reversed oscillatinglay (ROL) to create a core. The core is constructed so that the fiberbend radius exceeds 50 mm, the cable modulus of elasticity exceeds 800kpsi, and the fiber strain free window exceeds 0.25%, allowing shortterm tensile loads exceeding 600 lbs. A layer of polyethylene isextruded over the core to create outer jacket 4. The interior of theouter jacket 4 surrounding the core may be free from fillers such asgels or other tubes, members, etc. The cable 10 is designed to have acoefficient of thermal expansion less than 2×10⁻⁵/° C. and a contractionwindow in excess of 0.25%, allowing for operation at −40° C. withoutsignificant power loss. For constructions utilizing fibers with 250micron nominal diameter, the fiber density of the cable 10 may be 3.4fibers per mm². Alternatively, cable 10 constructions utilizing fiberswith 200 micron nominal diameter may have a fiber density of 4.8 fibersper mm². Fiber density as utilized herein is the ratio of the number offibers to the area of a circle that is equal to the outer diameter ofthe cable 10.

An ultra-high fiber density micro-duct cable consistent with exemplaryaspects of the present disclosure may have benefits and advantagesincluding but not limited to the following. The ultra-high density fiberoptic micro-duct cable allows the consumer to install a higher fibercount construction into an existing or newly installed duct, withoutsacrificing performance.

Furthermore, an ultra-high fiber density micro-duct cable may besuitable for use in a 13 mm inner diameter (ID) micro-duct. In order toqualify for use as a suitable 288 fiber count cable which is to be usedin a 13 mm ID micro-duct, exemplary experimentation, such asqualification testing, may be conducted. Qualification of the cable isbased, for example, on the requirements of Telcordia's GR-20-CORE Issue4 (GR-20), Generic Requirements for Optical Fiber and Optical FiberCable. The following experimental Examples are analyzed with respect toqualification for use in a 13 mm ID micro-duct.

Example 1

Example 1 is depicted in FIG. 2. A cable 100 of Example 1 is of a 288 fconstruction. The cable 100 comprises twelve buffer tubes 110, whicheach contain 24 fibers per tube and a gel. The fibers may be of 250micron nominal diameter. The buffer tubes 110 are cabled over a centermember 105 and collectively covered by an outer jacket 140. The centermember 105 includes an inner strength member, such as a fiberglassreinforced plastic rod, and an outer layer or up jacket of polyethylenethat is generally free from fiber reinforcement. The outer diameter ofcable 100 may be 12.8 mm, in which case, the cable 100 is typicallylimited to 15 mm ID micro-ducts.

Example 2

Example 2 is schematically similar to the cable depicted in FIG. 2 andis not separately illustrated. A cable of Example 2 is also of a 288 fconstruction. The cable comprises twelve buffer tubes, which eachcontain 24 fibers per tube and a gel, and two filler rods. The buffertubes and filler rods form a first layer and a second layer. The fibersmay be of 250 micron nominal diameter. The buffer tubes are cabled overa center member and collectively covered by an outer jacket. Compared toExample 1, a smaller center member is used. The outer diameter of thecable of Example 2 is 11.2 mm.

Example 3

Example 3 is depicted in FIG. 3. A cable 400 of Example 3 is also of a288 f construction. The cable 400 comprises eight buffer tubes 410,which each contain 36 fibers 420 per tube and a gel. The fibers may beof 250 micron nominal diameter. The buffer tubes 410 are cabled over acenter member 405 and collectively covered by an outer jacket 440. Theouter diameter of cable 400 is 11.8 mm.

Example 4

Example 4 is depicted in FIG. 4. A cable 500 of Example 4 is also of a288 f construction. The cable 500 comprises 3.1 mm outer diameter (OD),2.5 mm ID, gel filled, polybutylene terephthalate buffer tubes 510. Thecable 500 comprises six buffer tubes 510. Each buffer tube 510 contains48 colored fibers with two options for fiber identification. The firstoption is to use fibers with ring markings so that fibers #13-24 haveone ring, fibers #25-36 have two rings, and fibers #37-48 have threerings. Alternatively, fibers can be grouped into twelves and wrappedwith low denier, colored string binder threads. The six buffer tubes 510are SZ stranded over a central strength member 505 with a lay lengththat yields an actual fiber helical bend radius of greater than 40 mm,such as greater than 50 mm, and bound with uncoated polyester binders.Two water swell ripcords (not shown) are included under the outer, HDPEjacket 540. The nominal finished cable OD is 10.4 mm and the cable 500is intended for use in a 13 mm ID duct. The cable 500 can accommodatefibers with 200 micron nominal diameter or fibers with 250 micronnominal diameter.

Example 5

Example 5 is schematically similar to the cable depicted in FIG. 2 andis not separately illustrated. Furthermore, the cable of Example 5 isfor accommodating fibers with 200 micron nominal diameter, and thus usesbuffer tubes having an inner diameter of 1.6 mm and outer diameter of2.0 mm. The cable of Example 5 is substantially similar to that ofExample 2 except for the size of buffer tubes. Consequently, the outerdiameter of the cable of Example 5 is 11.2 mm.

Example 6

Example 6 is schematically similar to the cable depicted in FIG. 3 andis not separately illustrated. Furthermore, the cable of Example 6 isfor accommodating fibers with 200 micron nominal diameter, and thus usesbuffer tubes having an inner diameter of 1.9 mm and outer diameter of2.4 mm. The cable of Example 6 is substantially similar to that ofExample 3 except for the size of buffer tubes and core. Consequently,the outer diameter of the cable of Example 6 is 9.9 mm.

Example 7

Example 7 is schematically similar to the cable depicted in FIG. 4 andis not separately illustrated. Furthermore, the cable of Example 7accommodates fibers with 200 micron nominal diameter, and uses buffertubes having an inner diameter of 2.0 mm and outer diameter of 2.5 mm.The cable of Example 7 is substantially similar to that of Example 4except for the size of buffer tubes and core. Consequently, the outerdiameter of the cable of Example 7 is 8.7 mm.

The constructions of the above examples are summarized in the followingtables.

TABLE 1 Example 1 2 3 4 Fibers per Tube 24 24 36 48 # Tubes 12 12 8 6Tube Size (OD/ID) (mm) 2.3/1.8 2.3/1.8 2.9/2.3 3.1/2.5 Core Construction12@1 10@4@1 8@1 6@1 Core Outer Layer OD (mm) 11.8 10.2 10.8 9.4 Cable OD(mm) 12.8 11.2 11.8 10.4 Duct Fill % (13 mm ID) 98% 86% 91% 80%

Table 1 shows tube and core options for accommodating 250 μm OD fibers.Units of Tube Size and Core Outer Layer OD rows are millimeters. Itshould be noted that due to the fill %, relatively less run time, andneed for only a single cabling pass, Example 4 is a preferredconstruction for an ultra-high fiber density micro-duct cable suitablefor use in a 13 mm ID micro-duct.

TABLE 2 Example 4 5 6 7 Fibers per Tube 48 24 36 48 # Tubes 6 12 8 6Tube Size (OD/ID) (mm) 3.1/2.5 2.0/1.6 2.4/1.9 2.5/2.0 Core Construction6@1 12@1 8@1 6@1 Core Outer Layer OD (mm) 9.4 10.2 8.9 7.7 Cable OD (mm)10.4 11.2 9.9 8.7 Duct Fill % (13 mm ID) 80% 86% 76% 67%

Table 2 shows tube and core options for accommodating 200 μm OD fibers.Units of Tube Size and Core Outer Layer OD rows are in millimeters. Onthe basis of Table 2, it can be said that Example 4 is a preferredconstruction also for 200 μm OD fibers. Examples 6 and 7 also exhibitsuperior properties.

Testing of cables in accordance with the present disclosure have yieldedtest results indicating various advantages of the subject cablesrelative to prior art cables utilized in micro-ducts. In particular, theresults discussed herein were performed for a cable as described inExample 4. All tests described herein are in accordance with TelcordiaGR-20 specifications.

Mechanical testing of a test cable was performed. For example, fiberstrain was measured during application of a 600 pound tensile load inaccordance with Telcordia GR-20. The maximum fiber strain was below 0.6%(as required by Telcordia GR-20), such as below 0.3%, such as below0.2%, such as below 0.15%.

Additionally, compressive strength or crush testing was performedutilizing a 990 N load (as required by Telcordia GR-20 for standard,rather than micro-duct, cables). The Telcordia GR-20 limit for maximumchange in fiber attenuation during the compressive strength test is≦0.05 dB for 90% of the fibers and ≦0.15 dB for any fiber. The testresults yielded a maximum change in fiber attenuation of 0.05 dB, 0.04dB, or 0.02 dB, depending on the fiber type utilized.

Buffer tube kink diameter was also tested. The Telcordia GR-20 limit forbuffer tube kink diameter is less than or equal to 40 times the outerdiameter of the buffer tube. The test results yielded a buffer tube kinkdiameter of less than 70 millimeters, which is well within the requiredlimit for the subject cable.

Environmental testing of a test cable was additionally performed. Forexample, attenuation changes were measured at various temperaturesbefore and after cable aging in accordance with Telcordia GR-20. TheTelcordia GR-20 limit for attenuation change is a maximum fiberattenuation change of 0.15 dB/km and a maximum average fiber attenuationchange of 0.05 dB/km before cable aging, and a maximum fiber attenuationchange of 0.25 dB/km and a maximum average fiber attenuation change of0.1 dB/km after cable aging. The test results yielded maximum fiberattenuation changes and maximum average fiber attenuation changes duringa second −40 degree Celsius exposure before aging of less than 0.15dB/km, such as less than 0.14 dB/km. The test results further yieldedmaximum fiber attenuation changes and maximum average fiber attenuationchanges during a second −40 degree Celsius exposure after aging of lessthan 0.1 dB/km, such as less than 0.05 dB/km.

According to the above described exemplary embodiments, variousadvantages may be obtained, which include but are not limited to thefollowing: as discussed earlier, small diameter, lightweight cables withhigh fiber density are desired for use in micro-ducts. However, there isa competing requirement for sufficient tensile strength, crushresistance, and the like. The inventors have rigorously studied thefield of cables and have determined cables of exemplary embodiments ofthe instant disclosure satisfy the above needs and are suitable as a 288fiber count cable which may be used and jetted in a 13 mm ID micro-duct.Cables of exemplary embodiments may exhibit excellent operatingperformance, specifically, they can sustain high tensile load, have highcompression resistance and have wide operating temperature ranges.

The foregoing description of the exemplary embodiments is intended to beillustrative. Many alternatives, modifications, and variations will beapparent to those skilled in the art. Descriptions and features listedin relation to the foregoing exemplary embodiments are not to beconstrued as limiting the present inventive concept, the scope of whichis defined by the following claims.

What is claimed is:
 1. A micro-duct cable, comprising: a center member;a plurality of buffer tubes surrounding the center member; a geldisposed within each of the plurality of buffer tubes; a plurality ofoptical fibers disposed in each of the plurality of buffer tubes,wherein each of the plurality of buffer tubes has an outer diameter ofless than or equal to 3.1 millimeters and an inner diameter of less thanor equal to 2.5 millimeters and contains greater than or equal to 48optical fibers; and a cable jacket surrounding the plurality of buffertubes and the center member, wherein a maximum outer diameter of thecable is less than 13 millimeters and a modulus of elasticity of thecable is greater than or equal to 800 kpsi.
 2. The micro-duct cable ofclaim 1, wherein each of the plurality of buffer tubes has a compressionresistance of greater than or equal to 4.8 N/cm.
 3. The micro-duct cableof claim 1, wherein the cable has a coefficient of thermal expansion ofless than or equal to 2×10⁻⁵/° C. and a contraction window in excess of0.25%.
 4. The micro-duct cable of claim 1, wherein each of the pluralityof buffer tubes is formed from a polybutylene terephthalate.
 5. Themicro-duct cable of claim 1, wherein the cable jacket is formed frompolyethylene.
 6. The micro-duct cable of claim 1, wherein the opticalfibers are 250 micron nominal diameter optical fibers.
 7. The micro-ductcable of claim 1, wherein the optical fibers are 200 micron nominaldiameter optical fibers.
 8. The micro-duct cable of claim 1, whereineach of the plurality of buffer tubes contains 48 optical fibers.
 9. Themicro-duct cable of claim 1, wherein each of the plurality of buffertubes contains 72 optical fibers.
 10. The micro-duct cable of claim 1,wherein the cable has a fiber density of greater than or equal to 3.4fibers per mm².
 11. The micro-duct cable of claim 1, wherein the cablehas a fiber density of greater than or equal to 4.8 fibers per mm². 12.The micro-duct cable of claim 1, wherein the maximum outer diameter ofthe cable is less than or equal to 10.4 millimeters.
 13. The micro-ductcable of claim 1, wherein each of the plurality of buffer tubes has anouter diameter of 2.9 millimeters.
 14. The micro-duct cable of claim 1,wherein each of the plurality of buffer tubes has an outer diameter of2.4 millimeters.
 15. A micro-duct cable, comprising: a center member; aplurality of buffer tubes surrounding the center member; a plurality ofoptical fibers disposed in each of the plurality of buffer tubes,wherein each of the plurality of buffer tubes has an outer diameter ofless than or equal to 3.1 millimeters and an inner diameter of less thanor equal to 2.5 millimeters and contains greater than or equal to 48optical fibers; and a cable jacket surrounding the plurality of buffertubes and the center member, wherein a maximum outer diameter of thecable is less than 13 millimeters.
 16. The micro-duct cable of claim 15,wherein each of the plurality of buffer tubes has a compressionresistance of greater than or equal to 4.8 N/cm.
 17. The micro-ductcable of claim 15, wherein the cable has a coefficient of thermalexpansion of less than or equal to 2×10⁻⁵/° C. and a contraction windowin excess of 0.25%.
 18. The micro-duct cable of claim 15, wherein eachof the plurality of buffer tubes is formed from a polybutyleneterephthalate.
 19. The micro-duct cable of claim 15, wherein the cablejacket is formed from polyethylene.
 20. The micro-duct cable of claim15, wherein each of the plurality of buffer tubes contains 48 opticalfibers.
 21. The micro-duct cable of claim 15, wherein each of theplurality of buffer tubes contains 72 optical fibers.
 22. The micro-ductcable of claim 15, wherein the maximum outer diameter of the cable isless than or equal to 10.4 millimeters.
 23. The micro-duct cable ofclaim 15, wherein each of the plurality of buffer tubes has an outerdiameter of 2.9 millimeters.
 24. The micro-duct cable of claim 15,wherein each of the plurality of buffer tubes has an outer diameter of2.4 millimeters.